Scientists Seed Clouds to Make Rain

Critics may scoff and skeptics may laugh, but rainmakers are finally emerging from the backwaters of science.

For more than half a century scientists have experimented with wringing more water out of clouds and dumping that priceless moisture on the parched earth. Most have failed, or at least produced inconclusive results, but a mounting body of evidence now suggests that if done properly, cloud seeding can be effective.

Some areas, like Texas, have held in there despite the skeptics' sneers, and today cloud seeding is done over about a third of the Lone Star state, a region of some 45 million acres.

Texas claims to produce more rain, over a wider area, and for a longer duration because of its weather modification program, according to George Bomar, who wrote his doctoral dissertation on the subject in 1974. But why, then, hasn't the technology flooded the world?

"I think up until now the limiting factor has been our inability to engender substantive proof that the technology works, at least in the eyes of some in the meteorological community who remain skeptical," says Bomar, who administers the rain enhancement program for the Texas Natural Resource Conservation Commission.

But over the past few years the prestigious National Center for Atmospheric Research (NCAR) has been compiling evidence in hopes of getting to the bottom of the matter.

Encouraging Results

A team of scientists from the center spent three years seeding clouds in the drought-stricken northern Mexican state of Coahuila to see if they could finally answer the question of whether it works.

The answer seems to be a clear "yes," although support for a fourth and conclusive year of the project was dropped by the Mexican government because the drought came to an end. You might say it was cancelled because of rain.

Here's what the researchers found: Rainfall from seeded clouds lasted longer than rain from unseeded clouds, the rainfall covered a larger area, and total precipitation was higher, sometimes even doubled. And in many cases results began just 20 minutes after the seeding.

"We are very encouraged by the results," says lead scientist Roelof Bruinties of NCAR. The work in Mexico followed on the heels of a research project in South Africa in the early 1990s that reported similar results.

Bruinties is now in the United Arab Emirates conducting a three-month feasibility study to determine whether conditions there are right for a cloud seeding program.

"They have had a drought for the past four years and contacted us to conduct some research here in the possibility of rainfall enhancement via cloud seeding," Bruinties said by e-mail. "The field program started the beginning of January and will last until the end of March."

In addition to providing a scientific basis for evaluating cloud seeding, the NCAR project uses different elements as "seeds" to enhance rain formation in clouds, and that could turn out to be even more important than the scientific documentation.

Timing Is Everything

In nearly all other cases, tiny grains of silver are used as seeds. But the NCAR group is using a mixture of sodium, magnesium and calcium chloride, and it appears this type of seeding works better than silver in drought stricken areas.

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